Over the years, brachytherapy sources implanted into the human body have become a very effective tool in radiation therapy for treating diseased tissues, especially cancerous tissues. The brachytherapy sources are also known as radioactive seeds in the industry. Typically, these brachytherapy sources are inserted directly into the tissues to be irradiated using surgical methods or minimally invasive techniques such as hypodermic needles. These brachytherapy sources generally contain a radioactive material such as iodine-125 which emits low energy X-rays to irradiate and destroy malignant tissues without causing excessive damage to the surrounding healthy tissue, as disclosed by Lawrence in U.S. Pat. No. 3,351,049 ('049 patent). Because radioactive materials like iodine-125 have a short half-life and emit low energy X-rays, the brachytherapy sources can be left in human tissue indefinitely without the need for surgical removal. However, although brachytherapy sources do not have to be removed from the embedded tissues, it is necessary to permanently seal the brachytherapy sources so that the radioactive materials cannot escape into the body. In addition, the brachytherapy source must be designed to permit easy determination of the position and the number of brachytherapy sources implanted in a patient's tissue to effectively treat the patient. This information is also useful in computing the radiation dosage distribution in the tissue being treated so that effective treatment can be administered and to avoid cold spots (areas where there is reduced radiation).
Many different types of brachytherapy sources have been used to treat cancer and various types of tumors in human or animal bodies. Traditional brachytherapy sources are contained in small metal capsules, made of titanium or stainless steel, are welded or use adhesives, to seal in the radioactive material.
These various methods of permanently sealing the brachytherapy sources, used so that the radioactive materials cannot escape into the body and do not have to be removed after treatment, can have a dramatic effect on the manufacturing costs and on the radiation distribution of the brachytherapy sources. Increased costs reduce the economic effectiveness of a brachytherapy source treatment over more conventional procedures such as surgery or radiation beam therapy. In addition, the poorer radiation distribution effects, due to these sealing methods, in conventional brachytherapy sources may ultimately affect the health of the patient, since higher doses of radiation are required or additional brachytherapy sources must be placed inside the human body. All which leads to a less effective treatment that can damage more healthy tissue than would otherwise be necessary.
A first type of conventional brachytherapy source 10 is shown in FIG. 1, and uses two metal sleeves 12 and 14. The brachytherapy source 10 is disclosed in U.S. Pat. No. 4,891,165 issued Jun. 2, 1990 to Sutheranthiran and assigned to Best Industries of Springfield Va. Each of the sleeves has one closed end 16 and 18 using die-drawn techniques. Sleeve 14 has an outer diameter that is smaller than an inner diameter of the sleeve 12 to permit the sleeve 14 to slide inside sleeve 12 until the open end of sleeve 14 contacts the closed end 16 of the sleeve 12. Radioactive material, such as pellets, are placed inside the smaller sleeve 14, and then the larger external sleeve 12 is slid over the smaller sleeve 14. Next, the brachytherapy source 10 is permanently sealed by TIG (Tungsten Inert Gas) welding the open end of the larger sleeve 12 to the closed end 18 of the smaller sleeve 14. Laser welding may also be used. Although the welding of the two sleeves 12 and 14 together provides a good seal, the brachytherapy source 10 suffers from several drawbacks.
One drawback results from the radiation seed 10 being formed from two distinctly different sized pieces (the two sleeves 12 and 14), which involves an additional assembly step of fitting the two sleeves 12 and 14 together. This is time consuming and can slow the assembly process down, as well as increase the overall cost of producing the brachytherapy sources 10.
Another conventional brachytherapy source 30, as shown in FIG. 2, uses a single tube 32 which has end caps 34 and 36 inserted at the ends 38 and 40 of the single tube 32 to hold the radioactive material. The brachytherapy source 30 is disclosed in U.S. Pat. No. 4,784,116 issued Nov. 15, 1988 to Russell, Jr. et al. and assigned to Theragenics Corporation of Atlanta, Ga. The ends 38 and 40 are then welded, or adhesively secured, to the end caps 34 and 36 to close off and seal the brachytherapy source 30. Although the brachytherapy source 10 provides a single wall and a better radiation distribution along the length (or sides) of the brachytherapy source 30, the brachytherapy source 30 still suffers from several drawbacks.
A first drawback is that the ends 38 and 40 of the brachytherapy source 30 do not provide a uniform radiation distribution approximating a point source, because the end caps 34 and 36 provide a double wall at the end of the brachytherapy source 30 that blocks off a substantial amount of radiation. A further drawback results form the welds used to seal the end caps 34 and 36 to the ends 38 and 40 of the singe tube 32, since these also reduce the radiation distribution. Another drawback results from there being a three-step assembly process; rather, than the two step assembly process discussed above, since there are now three separate parts to be assembled together (the single tube 32 and the end caps 34 and 36).
In an alternative to this type of conventional brachytherapy source, a brachytherapy source 50, as shown in FIG. 3, has end plugs 52 and 54 that are slid into the open ends of a single tube 56. The brachytherapy source 50 is disclosed in U.S. Pat. No. 5,683,345 issued Nov. 4, 1997 to Waksman et al. and assigned to Novoste Corporation of Norcross, Ga. The end plugs 52 and 54 are either secured in place with an adhesive and the metal of the single tube 56 is then bent around the end plugs 52 and 54, or the end plugs 52 and 54 are welded to the single tube 56. The brachytherapy source 50 suffers from the same drawbacks as discussed above. In addition, the radiation distribution out the end plugs 52 and 54 is substantially reduced due to the added thickness of the end plugs 52 and 54.
In another conventional brachytherapy source 70, as shown in FIG. 4, some of the drawbacks of the multiple piece assembly are overcome by using a single tube 72 to provide a body with a uniform side wall along the length of the brachytherapy source 70. The brachytherapy source 70 is distributed by Amersham International PLC. One end 74 of the single tube 72 is TIG welded, and then the radioactive material is inserted into the open end 76 of the single tube 72. Next the open end 76 is TIG welded to seal the single tube 72 to provide a single unitary brachytherapy source structure. However, the brachytherapy source 70 suffers from many drawbacks.
For example, TIG welding the ends 74 and 76 causes formation of a bead of molten metal at the ends 74 and 76 of the single tube 72. Due to the nature of TIG welding the welded ends 74 and 76 generally form a bead that may be as thick as the diameter of the single tube 72. Therefore, the radiation distribution is substantially diminished out of the ends 74 and 76 of the brachytherapy source 72 due to the thickness of the beads 78 and 80 closing off the ends 74 and 76. In addition, the end 76 is only closed after the radioactive material is inserted into the single tube 72, and the end 76 may not seal in the same manner due to the presence of the radioactive material carrier body effecting the thermal characteristics of the brachytherapy source 70. Thus, the bead 80 can be a different shape than the bead 78, which may further alter the radiation distribution and could lead to inconsistent radiation distributions from one brachytherapy source to another, making the prediction of the actual radiation distribution more difficult.
Therefore, although the brachytherapy source 70 overcome some of the drawbacks in the earlier brachytherapy sources by minimizing the assembly steps associated with multiple pieces, it does not provide an even radiation distribution. In fact, due to the potential for variations of the second end during the TIG welding, the distribution can vary substantially from brachytherapy source 70 to brachytherapy source 70. Typical radiation distribution patterns for conventional brachytherapy sources 70 using the single tube 72 are shown in FIGS. 5(a) and 5(b). As is shown in FIGS. 5(a) and 5(b), the radiation distribution patterns 102 and 104 tend to diminish substantially toward the ends 74 and 76 of the brachytherapy source 70 and form cold zones 106 and radiation lobes 108. This means that depending on how the brachytherapy sources 70 are placed adjoining each other, there may be cold spots in the radiation distribution between adjoining brachytherapy sources 70, where cells are not receiving radiation from the cold zones 106 at the ends 74 and 76. Or if the adjoining brachytherapy sources are placed close enough together, to assure no cold spots from the presence of the cold zones 106, there will be overlapping areas in the radiation lobes 108 that may provide an excessive dose of radiation. Either of these two conditions could result in either too much or too little radiation, which results in a less effective medical treatment.